Free piston motor compressor



July 6, 1937. H JANICKE FREE PISTON MOTOR COMPRESSOR Filed Feb. 23, 1955 4 Sheets-Sheet v a; 33 g Inventor (4 1 a c t 0 Eu,

July 6, 1937. H. JANICKE FREE PISTON MOTOR COMPRESSOR Filed Feb. 23, 1935 4 Sheets-Sheet 2 Inventor. a Z; c

y 1937- H. JKNICKE FREE PISTON MOTOR COMPRESSOR Filed Feb. 23, 1935 4 Sheets-Sheet 5 H. JANICKE 2,086,162

FREE PISTON MOTOR COMPRESSOR Filed Feb. 23, 1935 4 Sheets-Sheet 4 .July 6, 1937.

Patented July 6, 1937 FREE PISTON MOTOR COIWPRESSOR Hermann Jiinicke, Dessau, Germany, assignor to Therese Junkers, Gauting, near Munich, Germany Application February 23, 1935, Serial No. 7,788

Germany March 9, 1934 13 Claims.

7 My invention relates to free piston motor compressors and has for one of its objects to provide means, whereby the output of such motor compressors can be varied within wide limits. In my copending U. S. application Serial No. 710,483 I have disclosed a methodof controlling a free piston motor compressor by varying the length of stroke and the pressures thereof, e. g. the suction or discharge pressure or a combina- 10 tion of both these'pressures. My copending U. S. application Serial No. 7,786 discloses the control of a free'piston motor compressor by means of a variation of the dead space and the fuel supply, while my copending U. S. application Serial No. 7,787 discloses the regulation of a free piston motor compressor by means of a variation of the pressures, i. e. the suction or delivery pressure or a combination of both these pressures, and of the fuel supply to the motor cylinder of ,the motor compressor.

In both the aforesaid U. S. applications Ser. Nos. 7,786 and 7,787 the variation of the fuel supply is adapted to the variation of the compressor output and is carried out in such a. manner that the length of the piston stroke always remains approximately constant.

.In free piston motor compressors comprising a combustion chamber and one or a plurality of compression chambers'and freely reciprocating pistons forming the freely movable mass it has been proposed, in order to control the output of the compressor, to change the length ofstroke of the movable mass, while the energy, by which the movable mass, after its working stroke, is

returned into its initial position (the so-called return energy) is kept constant. This change of stroke involves certain drawbacks in so far as the control of the internal combustion engine which is derived from the motion of the freely movable mass, is subjected to corresponding changes. Therefore a method of operation is desirable which allows varying within a wide range the output of the compressor and keeping the return energy approximately constant without substantially changing the stroke of the freely moving mass.

According to the present invention this is accomplished by simultaneously changing at least two of the variables which at a predetermined constant stroke of the piston determine the value of the quantity of gas discharged by the compressor (the output of the compressor) as well as of the energy fed by the compressor to the freely moving mass during the returnstroke (the return energy), these variables being chosen so as to afl'ect the output of the compressor in equal senses, the return energy in opposite senses, partly increasing and partly reducing this energy so that when the output changes the influences acting upon the return energy com- 5 pensate each other, this energy being kept approximately constant. The fuel delivery to the combustion chamber of the free piston compressor should be adapted to the output by means of hand-operated mechanism or, if desired, auto- '10 matically, for instance in dependency upon the stroke of the freely moving mass .or upon the pressure of the gas contained in a storage tank connected to the compressor.

The output of the compressor may be influ- 1 enced, for instance, by means of the following variables:

(a) The suction pressure, on the reduction of which the output is reduced as well as the return energy, 20

(b) The discharge pressure, on the increase of which the out-put will be reduced, while the return energy will increase,

(c) The part of the compression chamber utilized for discharging (the so-called efllcient dis- 5 charge volume), on .the diminution of which the output will be reduced, the return energy bein increased,

(d) The volume of the dead spaceof the compressor, on the increase of which the output is 30 reduced and the return energy increased.

Thus in varying the output of the compressor the return energy may be approximately kept constant by simultaneously changing, besides the value mentioned under (a), at least one of the 5 values (1)) to (d).

In free piston motor-compressors comprising a plurality of compression chambers these chambers may either be arranged so as to effect the compression in all chambers at a time or in some 40 chambers during the working stroke of the pistons, in the others during the return stroke.

In the case first mentioned the output of the compressor is controlled, according to this invention, by varying in the compression chambers 45 some of the variables in such manner that the amounts of return energy delivered by these chambers partly increase and partly decrease, while their sum total remains approximately constant. 50

In the second case the output of the compressor is controlled by changing in the several compression chambers those variables, the variation of which causes the return energy delivered from some of the chambers to the freely moving mass 55 during the return stroke to be changed in the same sense as the compression energy delivered to the other chambers by the freely moving mass during the same stroke. Thus these energies will decrease or increase together, the difference between them remaining approximately constant.

Besides the compression chambers there may further be provided auxiliary devices adapted for the storing or returning of energy, such as pneumatic or mechanical buffers for stabilizing the running of the compressor, scavenging pumps or the like. These auxiliary devices may either be arranged so as to feed energy or to withdraw energy from the freely moving mass during its return stroke. In pneumatic buflers the amount of this energy partly depends upon the same variables, viz. those mentioned hereabove under (0) and (d), as in the compression chambers, and further upon the amount (product of the pressure and volume) of the: gas enclosed in the buffer chamber. In mechanical (spring) buffers the amount of energy depends upon the mass of/and the load acting on the elastic material. Thus by varying one or a plurality of these values the amounts of'energy taken up or delivered by the buffers during the return stroke of the freely moving mass may be changed. Here again one or a plurality of the variables determining the output of the compressor and one or a plurality of the variables determining the energy taken up and/or delivered by the auxiliary devices are chosen to approximately keep constant at any output of the compressor the arithmetical sum total of the amounts of energy which during the return stroke are delivered to the freely moving mass (positive amounts) or are discharged by said mass (negative amounts), this sum representing the amount of energy available for the compression of the charge of air and fuel in the combustion chamber.

Still another means of compensating the variation of the return energy due to a change of output of the compressor consists in designing the motor portion of the free piston compressor in such manner that the energy taken up by it during the return stroke varies approximately in proportion to the return energy delivered by the compression chambers. This may be accomplished, for instance, by redischarging in a well known manner a greater or smaller part of ,the charge from the cylinder, before compression has started, through a discharge port held open for a suitable period of time.

The various means described hereabove for influencing the output of the compressor and the return energy may be combined with each other, if desired, in various ways.

In the drawings aflixed to this specification and forming part thereof some embodiments of my invention are illustrated diagrammatically by way of example. In the drawings Fig. 1 is an elevation, partly in axial section, of a free piston motor-compressor operating according to my invention, while Figs. 2-6 are pressure-volume diagrams serving to explain the operation of this compressor.

Figs. 7, 8, 10, 11, 13, 15, and 16 are elevations, partly in axial section, of further embodiments of this invention, each figure representing only one half of the compressor.

Fig. 9 is a cross section, drawn to a larger scale along the line IX-IX in Fig. 8.

Figs. 12 and 14 are pressure-volume diagrams serving to explain the operation of buifers operating according to my invention.

Referring to the drawings and first to Fig. 1, the free piston motor-compressor here shown comprises a casing I, the mid-portion of which forms a combustion chamber 2, while a compression chamber 3 is provided at each end of the casing. There are further provided a pair of free pistons or freely moving masses, each comprising a motor piston 4 and a compressor piston 5 directly connected with each other. 6 and I are scavenging and exhaust ports, respectively, provided in the wall of the casing I and controlled by the motor pistons 4.' The compressor pistons 5, during the return stroke, draw in through suction valves 8 the gas which is compressed during the working stroke and discharged through pressure valves 9, pressure pipes I 0, and collecting pipe II to storage tank [3 from which it is n discharged to the consumer (not shown) through a pipe l4. I2 is a spring-loaded non-return valve provided in the collecting pipe II, by which the pressure in the compressor chambers 3 at the close of the compression will be maintained at a predetermined minimum value even if in consequence of the discharge of great quantities of gas the pressure in the tank l3 should drop below the said minimum value. The load on the valve I2 is so chosen that the corresponding final pressure of compression, upon which depends the amount of return energy, affords a return energy which suffices for warranting correct operation of the compressor. Valve l2 may be dispensed with if the pressure valves 9 are designed in such manner that they will be open only when the final pressure of compression reaches the minimum value required for warranting correct operation of the compressor. The gas remaining over in the dead. spaces of the compression chambers, at the end of the working stroke in expanding, forces the masses 4. 5 towards each other. As soon as the pressure in the compression chambers has dropped to become equal to the suction pressure, fresh gas will be drawn in through the suction valves 8. At the same time the mixture in the combustion chamber 2 is compressed, fuel being delivered to said chamber by a suitable device l6, for instance, an injection nozzle. The charge is ignited and the products of combustion drive the masses asunder, whereby thegas in the compression chambers is compressed and discharged. In order to secure synchronous reciprocation of the freely moving masses, they are connected with each other bya suitable gearing such as racks l1 secured to the masses and engaging a pinion l8 rotatably mounted on the casing I.

Fig. 1 shows in dotted lines the dead centre positions of the pistons 5, s indicating the length of stroke which should be kept constant, as far as this is possible in view of the unavoidable slight variations of the stroke of the pistons, at any output of the compressor, which may vary within a wide range, from maximum discharge to zero.

This device operates as follows:

Fuel is periodically delivered to the combustion chamber 2 at the end of the return strokes of the pistons. The charge in the motor cylinder, after having been compressed, is ignited whereby the pistons 4, 5 are driven from their inner to their outer dead centre positions, the gearing ,l 1, I8 providing for an exactly synchronous movement of the pistons.

During the outward (working) stroke the gas in the compression chambers 3 is compressed to the discharge pressure and is discharged through the valves 9 and pipes l0 and II to tank l3. During the latter part of the working stroke the exhaust ports I and scavenging ports 6 are opened so that fresh air can enter the combustion chamber 2 and the exhaust gases are discharged. The compressed gas remaining in the dead spaces of the compression chambers 3 at the end of the working stroke now re-expands and returns the pistons to their inner dead centre positions, fresh gas being drawn in through the suction valves 8 during the latter part of the return stroke. When the pistons have reached their inner dead centre positions, the cycle of operations is repeated.

Figs. 2-6 illustrate the manner in which by varying several determining variables, the output of the compressor and the amount of return energy may be influenced. In these figures the cycle ABCDA represents the compressor diagram at normal output, the gas being compressed from the suction pressure 221 to the discharge pressure 122. The return energy is represented by the area CDAEFC.

Fig. 2 illustrates the controlling of the output by reducing the suction pressure. A2B1CD2A2 is the diagram corresponding to the reduced suction pressure p11. The output is represented by the distance 310 which is smaller than the distance BC representing the normal output. The return energy corresponding to the reduced output is represented by the area CDzAzEFC which is smaller than the normal return energy by the amount DAAzDzD.

Fig. 3 illustrates the controlling of the output by increasing the discharge pressure. pressure is increased, for instance, to pm, the diagram AB2C2D1A will be obtained, the suction length D1A of which is smaller than the suction length DA corresponding to the normal output. In a similar proportion the amounts of gas will be changed which are drawn in and discharged.

The return energy corresponding to the reduced output is represented by the area C2D1AEFC2 which exceeds the normal return energy by an amount corresponding to the area C2D1DCC2.

Fig. 4 illustrates the controlling of the output by allowing part of the previously compressed and discharged gas to flow back into the compression chambers. By thus reducing the'output the starting point of the re-expansion is shifted from C to H. Re-expansion occurs along the curve HJ. There is thus obtained the diagram return energy by the area CLDC.

Now the return energy may be kept approximately constant by simultaneously employing a plurality of controlling means which partly increase and partly reduce the return energy. An example of a control of this kind is shown in Fig. 6 which illustrates the simultaneous application of the modes of control shown in Figs. 2' and 3,

If this viz. the reduction oi! the suction pressure and the increase of the discharge pressure. Here compression starts at the reduced suction pressure p11 and goes on, till the increased discharge pressure pn is reached, and the diagram AaBzCaDzAa is obtained. The return energy' is increased by the area C2D1DCC2 and reduced by the area DiAAzDaDi. If the control is carried through in such manner that these last two areas are equal, the return energy will remain constant. If desired, the means oi! control according to Figs. 4 and 5 may be used singly or in combination with each other, similarly as the means shown in Fig. 3, together with the reduction of the suction pressure according to Fig. 2.'

Fig. 7 shows means for influencing the output of the compressor by varying the suction pres sure. All the suction valves 8 are connected to a common suction pipe 2| containing a slide 22 connected to a piston 23 which is loaded, through pipe 24, with the pressure in the tank l3 tending to close the slide against the force of a spring The compression chamber 3 and an annular chamber 30 into which discharge the pressure valves 9, are connected with each other by a port 3| which may be opened and closed by means of a slide 32 actuated by a cam 33 mounted on the rack II, a crank lever 34 and a rod 35. The cam 33 is undisplaceably, but rotatably secured to the rack ll, its protruding portion having different lengths in diflerentradial planes so that by turning the cam the movement of the slide may be varied. As shown in Fig. 9, this may be efiected by'means of an arm 36 secured to the cam and engaging. all through its stroke along with the rack I! a channel 31 extending in parallel to the rack II. The channel 31 is transversely adjustable, for instance in dependency on the pressure in the tank l3 by means of a piston 38 acted upon by this pressure and against the action of a spring 39. When it is desired to make the compressor operate at its maximal output, the cam 33 is adjusted in such manner that the slide 32 is not shifted and keeps the port 3| permanently closed. In order to reduce the output of the compressor the cam 33 is turned so that the slide 32 isdisplaced and the port 31 is opened when the compressor piston 5 approaches the dead centre position corresponding to the discharge end. On reversal of the movement of the piston compressed air will flow back from the chamber 30 to the compression chamber 3 until during the return stroke of the piston 5 the cam 33 comes out of reach of the crank lever 34.

, Fig. 10 illustrates a device for influencing the output of the compressor by changing thevolume of the dead space. The endwall 40 of the compression cylinder is formed with a cylindrical extension 4| in whicha piston 42 is slidably arranged. The rod 43 of the piston 42 is formed with a thread 44 engaged by the internally threaded hub of a toothed wheel 45 which is axially undisplaceable and engaged by the toothed rod 46 of a piston-41 acted upon by the pressure in the tank l3 against the action ,of a spring 48. When the pressure in the tank l3 exceeds its normal value, i. e. when the output of the compressor exceeds the demand for com- 'pressed gas, the piston 41 is forced downwardly against the action of the spring", the toothed wheel 45 being rotated and shifting the piston 42 to the right, thereby increasing the dead space of the compression cylinder and correspondingly reducing the output.

In the embodiments shown in the following figures there are provided, besides the compression chambers, auxiliary chambers; such as buffers or the like which are connected with devices for influencing the return energy available for the compression of the charge in the combustion chamber.

In the embodiment shown in Fig. 11 a buffer connected to the compressor and comprising a cylinder 5| and piston 52 takes up energy during the working stroke and feeds it back during the return stroke. The end wall of the cylinder 5| is formed by a piston 53 allowing the volume of the dead space of the buiIer to be varied. The piston 53 may be adjusted by hand or, if desired,

automatically in dependency on the pressure in the tank in a similar manner as shown in connection with the piston in Fig. 10.

Fig. 12 illustrates the diagram of the buffer shown in Fig. 11. The initial pressure is always equal to no. If this pressure is equal to that of the atmosphere, a small port 54 in'the wall of the buffer cylinder near the dead centre position corresponding to the beginning of the workind stroke will be sufilcient for maintaining this pressure. With a small dead space or of the buffer compression will occur along the curve MN, the return energy fed by the buffer corresponding to the area NPQMN. If the dead space of the buffer is increased by the amount v'-r, compression will occur along the curve MR situated beneath the curve MN, the return energy of the buffer being reduced to the area RPQMR.

If the return energy fed by the compressor decreases, as the output is reduced, for instance in throttling the gas drawn in by the compressor according to Figs. 2 and 7, the portion of the return energy which is fed by the buffer, must increase. In that case the device shown in Fig. l1 should be designed in such manner that the dead space of the buffer decreases when the output of the compressor drops, and vice versa. v

If, on the other hand, the return energy of the compressbr increases on the output being reduced, for instance according to Figs. 3-5, the dead space of the butler must become smallersas the output drops.

Fig. 13 illustrates another embodiment of a device for varying the portion of the return energy fed by the buffer. The working chamber 55 of the cylinder 5| of the buffer is formed with a port 56 in the cylinder wall near the inner dead centre position of the piston, this port connecting the working chamber to a pipe 51 leading to the tank l3.

The operation of this device will be understood from the diagram shown in Fig. 14. If the pressure in the tank l3 has its normal value pm, the compression in the chamber 55 of the buffer will occur along the curve ST. If, however, the pressure in the tank l3 rises to the value ps, the curve of the compression is represented by UV, the return energy fed by the buffer being increased by the amount corresponding to the area VTSUV.

A buffer, an additional compressor or the like may be provided, if desired, to take up energy (negative return energy) during the return stroke of the freely moving mass and to feed this energy back during the working stroke. If the compressor piston is larger than the motor piston (as is shown in Fig. 1), the differential piston surface and the chamber ill, in which the latter runs, may constitute a bufler or an additional compressor. The amount of energy taken up by this buffer or additional compressor during the return stroke of the freely moving mass may be varied, in dependency on the variation of output of the compressor, by means such as described hereabove in connection with the ordinary buffer or the main compressor, to afford a resultant return energy which is at leastapproximately constant.

An example of such an embodiment is shown in Fig. 15. The chamber 60 adjoining the left hand side of the compressor piston 5 is designed as a scavenging pump and provided with suction valves 6| and pressure valves 52. A pipe 83 connecting the pressure valve 52 to a scavenging air tank 64 shown in Fig. 16 is provided with a throttling device 55 actuated by the pressure in the tank ii in a similar manner as described hereabove in connection with Fig. 7, exerting a throttling action in proportion as this pressure increases, and vice versa. If desired, the throttling device may also be adjusted by means of a hand-operated device.

Fig, 16 illustrates means for varying the taking up of energy in the combustion chamber. 10 are ports arranged in alignment in the wall of the cylinder I near the scavenging ports 5. They may be covered or uncovered by a slide II connected to apiston I4 displaceably arranged in a cylinder 12 and acted upon on one side by the pressure in the tank and on the other by a spring I3.

The output of the compressor shall be reduced as the pressure in the tank I 3 rises.

If the compressor is adjusted in such manner that the return energy increases when the output is reduced, for instance as illustrated in Figs. 3-5, the slide II and the piston should be arranged, as shown in the drawing, in such manner that on the pressure in the tank l3 rising the ports II are closed one after the other by the slide ll, whereby a steadily decreasing part of the charge will be returned into the scavenging air tank before being compressed, so that the energy required for compression is increased correspondingly.

If the compressor is controlled by throttling the suction according to Fig. 2, the return energy will drop when the output is reduced. In this case the slide II and the piston 14 should be arranged to uncover the ports lll one after the other when the pressure in the tank l3 rises, and the amount of charge subjected to compression and the energy required for this compression will then decrease correspondingly. This mode of control is particularly recommendable since the quantity of the charge is varied in the same sense as the output to be delivered by the motor portion of the compressor.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim:

1. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either. side rectly connected with each other, means for varying at least two of the variables determining the taking up and delivery of energy in said compressor cylinder in such manner that the energy available for compression of the motor charge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant. I

2. A free piston motor compressor comprising in combination, a motor cylinder, a main and an additional compressor cylinder arranged on either side thereof, a free piston in each of said cylinders, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected, with each other, means for varying at least two of the variables determining the taking up and delivery of energy in the said main and additional compressor cylinders in such manner that'the energy available for compression of the motor charge remains approximately constant, and means for' at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant. v

3. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected with each other, means for varying the discharge pressure and at least one other variable determining the taking-up and delivery of energy in said compressor cylinder in such manner that the energy available for compression of the motor charge remains approximately. constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

4. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected with each other, means for varying the suction pressure and at least one other variable determining the taking up and delivery of energy in said compressoricyllnderin such manner that the energy available for compression of the motor charge remains approximately constant, and means for at the same tim varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

5. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected with each other, means for varying the useful discharge volume and at least one other variable determining the taking up and delivery of energy in said compressor cylinder in such manner that the energy available for compression of the motor charge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

6. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected with each other, means for vary- "ing the clearance volume and at least one other variable determining the taking up and delivery of energy in said compressor cylinder in such manner that the energy available for compression of the motor charge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

7. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side'of the motor cylinder being directly connected with each other, means for varying at least two of the variables determining the output of the compressor and the variations of which influence the feed-back energy in opposite senses, in such manner that the energy available for compression of the motorcharge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

8. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the'motor cylinder being directly connected with each other, means for varying the suction and discharge pressures in said compressor cylinder in opposite senses and in such manner that the energy available for compression of the motor charge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length ofthe piston stroke remains substantially constant.

9. A free piston motor compressor comprising in combination, a, motor cylinder, a plurality of compressor cylinders arranged on either side thereof for compression during the motor working stroke, a free piston in each of said cylinders, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected with each other, means for varying at least two of the variables determining the taking up and delivery of energy in the said compressor cylinders in such manner that the feed-back energy in part of said compressor cylinders is increased and in another part of said cylinders reduced in such manner that the energy available for compression of the motor charge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

10. A free piston motor compressor comprising in combination, a motor cylinder, a plurality of compressor cylinders arranged on either side thereof, one on either side being arranged for the compression to take place during the motor working stroke, while another one on the same side is arranged for compression to take place during the return stroke, a free piston in each of said cylinders, said pistons being operatively connected with each other, means for varying at least two of the variables determining the taking up and delivery of energy in the said compressor cylinders in such a manner that the amounts of energy delivered during the return stroke in one of said compressor cylinders vary in the same sense as the amounts of energy taken up during the return stroke in another compressor cylinder and that 10 the difference of energy available for compression of the motor charge is substantially constant independently from the output, and means for at the same time varying the supply of fuel to the said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

11. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder. being directly connected with each other, a buffer arranged to deliver the energy, accumulated during the working stroke, again during the return stroke, means for varying at least one of the variables determining the output of the said compressor and at least one of the variables determining the taking up of energy of the said buifer in such manner that the resulting amount of energy'available for the compression of the motor charge remains approximately constant, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

12. A free piston motor compressor comprising in combination, a motor cylinder and at least one compressor cylinder arranged on either side thereof, a free piston in each cylinder, comprising a motor piston and a compressor piston arranged on the same side of the motor cylinder being directly connected with each other, means for regulating the output of said compressor, means for varying the resistance energy to be overcome in said motor cylinder on the return stroke to substantially the same extent as the feed-back energy is varied by the variation of the output, and means for at the same time varying the supply of fuel to said motor cylinder in such manner that the length of the piston stroke remains substantially constant.

13. The free piston motor compressor of claim 12 in combination with means connected with the motor cylinder for enabling part of the motor cylinder charge to be discharged before compression is started.

HERMANN JANICKE. 

